TFTs utilizing silicon semiconductors or compound semiconductors are used in common integrated circuits and in wide-spreading other applications. In particular, the use of TFTs in liquid crystal displays is well known. Nowadays LC displays are making continuous progress toward larger size and more precise definition. The requirement to incorporate a greater number of TFTs corresponding to the number of pixels becomes stronger than ever.
However, ordinary metal based semiconductors used in the art cannot avoid the problem that slight defective pixels are caused by the defects of TFTs formed on the substrate as a result of treatments including patterning and etching using photoresists during circuitry formation on the substrate. Such treatments impose a certain limit in reducing the cost of TFT manufacture. This is also true for other flat displays such as plasma displays and organic EL displays when TFTs are used therein.
The recent trend toward larger size and more precise definition tends to increase the probability of defection in the TFT manufacture. It is thus strongly desired to minimize such TFT defects.
For TFTs with a metal-insulator-semiconductor (MIS) structure, attempts have been made to use organic materials as the insulator and semiconductor. For example, JP-A 5-508745 (WO 9201313 or U.S. Pat. No. 5,347,144) describes that a device using an insulating organic polymer having a dielectric constant of at least 5 as the insulating layer and a polyconjugated organic compound having a weight average molecular weight of up to 2,000 as the semiconductor layer exerts a field effect and has a mobility of carriers of about 10−2 cm2V−1s−1. Since the semiconductor layer is formed by evaporating α-sexithienyl as an organic semiconductor material, treatments including patterning and etching using photoresists are necessary, failing to achieve a cost reduction.